Melting Point Of Milk Fat Research Articles

Use of high doses of 18:0 to try to mitigate the syndrome of milk fat depression in dairy ewes fed marine lipids

Despite the benefits of adding marine lipids rich in n-3 polyunsaturated fatty acids (PUFA) to ruminant diets to improve milk fatty acid (FA) composition, this strategy induces milk fat depression (MFD), precluding its application under practical conditions. The MFD elicited by marine lipids has tentatively been explained by a shortage of available ruminal 18:0 for mammary uptake and Δ9-desaturation to cis-9 18:1, which might increase milk fat melting point and impair fat secretion. This hypothesis was challenged in a recent experiment in dairy ewes, as diet supplementation with 2% DM of 18:0 did not prove useful to alleviate fish oil-induced MFD. However, further research with higher levels of 18:0 inclusion seemed advisable. Therefore, in this study, 16 lactating ewes were allocated to 4 treatments lasting 27days: a total mixed ration containing no additional lipid (control) or 2% DM of fish oil alone (FO) or in combination with 3% (FOSA3) or 4% (FOSA4) of stearic acid. Fish oil supplementation induced MFD, but addition of 18:0, regardless of the dose, was not able to mitigate it: decreases in milk fat content reached 19% in FO, 20% in FOSA3 and 27% in FOSA4. The reduction in milk 18:0 concentration due to FO (−81%) was completely reverted neither by FOSA3 (−41%) nor by FOSA4 (−25%), and something similar occurred with cis-9 18:1 concentrations (12.53, 5.91, 9.50 and 11.28g/100 FA, in control, FO, FOSA3 and FOSA4, respectively). Increases in some candidate milk fat inhibitors in FO and FOSA diets (e.g., cis-9 16:1, cis-11 18:1, trans-10 18:1, 10-oxo-18:0, or trans-10 cis-15 18:2) might account for the absence of a positive effect of dietary 18:0. The estimated milk fat melting point was lower in the three supplemented diets (on average, −2.6°C compared with the control). In conclusion, addition of high doses of stearic acid to the diet (at 3 and 4% DM) was not able to alleviate the MFD caused by the concomitant supplementation with fish oil. This lack of response would further challenge the hypothesis suggesting that fish oil-induced MFD is mainly explained by decreased ruminal production of 18:0 and subsequent problems of milk fat fluidity, but further research would be still needed.

Comparison of milk fatty acid responses during fish oil- and trans-10 cis-12 18:2-induced milk fat depression in dairy ewes

The direct comparison between milk fat depression (MFD) caused by the addition of trans-10 cis-12 18:2 (a conjugated linoleic acid – CLA – isomer) or marine lipids to the diet of dairy ewes may help to elucidate the origin of this syndrome. Therefore, 12 lactating sheep were divided in 3 lots and offered a diet without supplementation (control) or supplemented with 2% DM of fish oil (FO) or 1.1% DM of a rumen-protected product rich in trans-10 cis-12 18:2 (CLA) for 27 days to compare the responses in terms of animal performance and milk fatty acid (FA) profile. Both supplemented diets (FO and CLA) decreased the milk fat content in a similar manner (−18% compared with the control). On the other hand, responses in milk FA profiles differed significantly and support that marine lipid-induced MFD is not mediated by the effects of trans-10 cis-12 18:2. However, a comparison of changes in the molar production of milk FA show that de novo FA synthesis was affected similarly in FO and CLA treatments and more strongly than FA uptake, which implies that both types of MFD might share common mechanisms. The results point to the involvement of less well-known potentially antilipogenic metabolites (such as intermediates of 18:3n−3 biohydrogenation or ruminal hydration and oxidation) in the low-milk fat syndrome in ewes fed FO and seem to downplay the relevance of changes in the milk fat melting point as a major mechanism responsible for FO-induced MFD.

Comparison of the nutritional regulation of milk fat secretion and composition in cows and goats

A study with 2 ruminant species (goats and cows) with inherent differences in lipid metabolism was performed to test the hypothesis that milk fat depression (MFD) due to marine lipid supplements or diets containing high amounts of starch and plant oil is caused by different mechanisms and that each ruminant species responds differently. Cows and goats were allocated to 1 of 3 groups (4 cows and 5 goats per group) and fed diets containing no additional oil (control) or supplemented with fish oil (FO) or sunflower oil and wheat starch (SOS) according to a 3×3 Latin square design with 26-d experimental periods. In cows, milk fat content was lowered by FO and SOS (−31%), whereas only FO decreased milk fat content in goats (−21%) compared with the control. Furthermore, FO and SOS decreased milk fat yield in cows, but not in goats. In both species, FO and SOS decreased the secretion of <C16 and C16 fatty acids (FA), and FO lowered >C16 FA output. However, SOS increased milk secretion of >C16 FA in goats. Compared with the control, SOS resulted in similar increases in milk trans-10,cis-12 conjugated linoleic acid (CLA) in both species, but caused a 2-fold larger increase in trans-10 18:1 concentration in cows than for goats. Relative to the control, responses to FO in both species were characterized by a marked decrease in milk concentration of 18:0 (−74%) and cis-9 18:1 (−62%), together with a ~5-fold increase in total trans 18:1, but the proportionate changes in trans-10 18:1 were lower for goats. Direct comparison of animal performance and milk FA responses to FO and SOS treatments demonstrated interspecies differences in mammary lipogenesis, suggesting a lower sensitivity to the inhibitory effects of trans-10,cis-12 CLA in goats and that ruminal biohydrogenation pathways are more stable and less prone to diet-induced shifts toward the formation of trans-10-containing intermediates in goats compared with cows. Even though a direct cause and effect could not be established, results suggest that regulation of milk fat synthesis during FO-induced MFD may be related to a shortage of 18:0 for endogenous mammary cis-9 18:1 synthesis, increase in the incorporation of trans FA in milk triacylglycerols, and limitations in the synthesis of FA de novo to maintain milk fat melting point. However, the possible contribution of biohydrogenation intermediates with putative antilipogenic effects in the mammary gland, including trans-9,cis-11 CLA, trans-10 18:1, or cis-11 18:1 to FO-induced MFD cannot be excluded.

Dietary fish oil supplements depress milk fat yield and alter milk fatty acid composition in lactating cows fed grass silage-based diets

The potential of dietary fish oil (FO) supplements to increase milk 20:5n-3 and 22:6n-3 concentrations and the associated effects on milk fatty acid (FA) composition, intake, and milk production were examined. Four multiparous lactating cows offered a grass silage-based diet (forage:concentrate ratio 58:42, on a dry matter basis) supplemented with 0, 75, 150, or 300g of FO/d (FO0, FO75, FO150, and FO300, respectively) were used in a 4×4 Latin square with 28-d experimental periods. Milk FA composition was analyzed by complementary silver-ion thin-layer chromatography, gas chromatography-mass spectrometry, and silver-ion HPLC. Supplements of FO decreased linearly dry matter intake, yields of energy-corrected milk, milk fat and protein, and milk fat content. Compared with FO0, milk fat content and yield were decreased by 30.1 and 40.6%, respectively, on the FO300 treatment. Supplements of FO linearly increased milk 20:5n-3 and 22:6n-3 concentrations from 0.07 to 0.18 and 0.03 to 0.10g/100g of FA, respectively. Enrichment of 20:5n-3 and 22:6n-3 was accompanied by decreases in 4- to 18-carbon saturated FA and increases in total conjugated linoleic acid (CLA), trans FA, and polyunsaturated FA concentrations. Fish oil elevated milk fat cis-9,trans-11 CLA content in a quadratic manner, reaching a maximum on FO150 (from 0.61 to 2.15g/100g of FA), whereas further amounts of FO increased trans-10 18:1 with no change in trans-11 18:1 concentration. Supplements of FO also resulted in a dose-dependent appearance of 37 unique 20- and 22-carbon intermediates in milk fat. Concentrations of 16-, 18-, 20-, and 22-carbon trans FA were all increased by FO, with enrichment of trans 18:1 and trans 18:2 being quantitatively the most important. Decreases in milk fat yield to FO were not related to changes in milk trans-10,cis-12 CLA concentration or estimated milk fat melting point. Partial least square regression analysis indicated that FO-induced milk fat depression was associated with changes in the concentrations of multiple FA in milk. Even though a direct cause and effect could not be established, a decrease in 18:0 supply in combination with increased mammary uptake of cis-11 18:1, trans-10 18:1, and trans 20- and 22-carbon FA may contribute. In conclusion, dietary FO supplements enrich 20:5n-3 and 22:6n-3 in milk, but also elevate mono- and polyenoic trans FA concentrations, and in high amounts alter the distribution of individual trans FA isomers.

Goat alpha-s1 casein genotype interacts with the effect of extruded linseed feeding on milk fat yield, fatty acid composition and post-milking lipolysis

This study compares two groups of 23 and 24 goats with different CSN1S1 genotypes, matched for lactation number and stage. During the first experimental period (4 weeks) half of the goats of each genotype received the control diet (CT) and the second half received a similar diet containing extruded linseed (EL diet). During the second experimental period, the two groups of goats were switched from the CT to the EL diet and from the EL to the CT diet, respectively. Results confirm the lower milk protein (−4.8g/kg) and fat (−6.5g/kg) concentrations in the low genotype group, whereas milk yield was slightly higher (+0.49kg/d) and lactose concentration was unchanged. Between the genotype groups, there were differences in milk fat proportions of at least 25 FAs, particularly the C7 to C13 saturated FAs and C16:0, C18:0, C18:2n-6 and cis9,trans11-C18:2 acids. In addition, delta-9 desaturation ratios were higher in the low CSN1S1 group for C10:0, C14:0, C18:0, trans11-C18:1 and trans13-C18:1. This strongly suggests an effect on mammary delta-9 desaturase activity, especially for C18:0 and trans11-C18:1. It is likely that higher desaturation ratios in the low genotype, as well as observed changes in other FAs, could compensate for the lower synthesis of medium-chain FAs (C7:0–C13:0), thus contributing to maintenance of the melting point of milk fat in this genotype. The effect of the EL diet on milk FA proportions was highly significant for almost all FAs, along with increased milk fat content and decreased post-milking free FA concentration. Numerous interactions (significant but of limited quantitative extent) between the CSN1S1 genotype and EL feeding were shown on milk composition, including 26 FA proportions or delta-9 desaturation ratios, and post-milking free FA concentration.

Short communication: Diet-induced variations in milk fatty acid composition have minor effects on the estimated melting point of milk fat in cows, goats, and ewes: Insights from a meta-analysis

In ruminants, the ability to maintain milk fat melting point within physiological values could play a role in the regulation of milk fat secretion when milk fatty acid (FA) composition varies, such as in response to feeding factors. However, the relationship between milk fat fluidity and changes in milk FA composition is difficult to study experimentally. A meta-analysis was therefore conducted to compare the magnitude of diet-induced variations in milk FA composition and the calculated melting point of milk FA (used as a proxy to estimate the variations in the melting point of milk fat) in 3 dairy ruminant species (cow, goat, and sheep). The coefficient of variation (CV), a scale-free measure of statistical dispersion, was used to compare the variability of criteria differing in their order of magnitude. The analysis of a database of milk FA profiles from cows, goats, and sheep fed different dietary treatments (unsupplemented diets and diets supplemented with lipids rich in oleic acid, linoleic acid, linolenic acid, or C20–22 polyunsaturated FA) revealed that the variability of the calculated melting point of milk FA was narrow (CV of 5%) compared with the variability of milk FA percentages (CV of 18 to 72%). The regulation of the melting point of milk fat is thus probably involved in the control of diet-induced variations in milk fat secretion. The calculated melting point of ewe milk FA was approximately 3°C lower than that of goats or cows across all types of diets, which might be linked to differences in milk fat content (higher in sheep) or the structure of milk triacylglycerides among these species. Lipid supplementation increased the calculated melting point of C18 FA in milk, whereas that of total FA was significantly reduced by supplements rich in oleic, linoleic, and linolenic acids but not C20–22 polyunsaturated FA. However, the slight effects of dietary treatments on the calculated melting point of milk FA did not differ between cows, goats, and ewes.

Goat's alpha-s1 casein genotype influences its milk fatty acid composition and delta-9 desaturation ratios

A large number of studies about impacts of alpha-s1 (αs1) casein (CSN1S1) gene polymorphism on goat milk composition, including its milk fat concentration, secretion in mammary cells and transcriptome analysis, have been reported. Despite this knowledge, very little data is available on the fatty acid (FA) composition of goat milk according to the CSN1S1 genotype. The study reported here compares two groups of 33 and 38 goats with different CSN1S1 genotypes, associated respectively with low or high milk protein and fat concentrations, matched for lactation stage and diets. Results confirm the lower milk protein (−5.0 g/kg) and fat (−6.8 g/kg) concentrations in the Low genotype group, whereas milk yield and its lactose concentration were not changed. There were between-group differences in proportions in milk fat of at least 17 FA, particularly the C8–C12 saturated FA and palmitic, stearic, oleic, linoleic and rumenic acids. In addition, delta-9 desaturation ratios were higher in the Low CSN1S1 group for C10:0, C14:0, C17:0, C18:0, trans11-C18:1 and trans13-C18:1, which strongly suggests an effect on mammary desaturase activity, especially for C18:0 and trans11-C18:1. It is likely that higher delta-9 desaturation ratios for C10:0 to transC18:1 isomers in the Low genotype could compensate for the lower secretion of medium-chain FA (C8:0 to C12:0), thus contributing to maintenance of the melting point of milk fat in this genotype. The polymorphism in the CSN1S1 genotype has important impacts on goat milk fat, and its FA composition, possibly making the goat model of interest in the search for a better understanding of regulation of mammary function, in particular FA synthesis, desaturation and secretion, and how it could be related to protein synthesis and secretion.

Salt-induced structural changes in 1-day old Mozzarella cheese and the impact upon free oil formation

Abstract Mozzarella cheese was manufactured to different salt levels by either a combination of dry- and hot-brine salting, or by cold-brine salting alone. Dry- and hot-brine salting resulted in a higher moisture content compared to cold-brine salting at equivalent salt levels. Increasing levels of salt with either salt treatment decreased the amount of expressible serum, increased apparent viscosity, but had no effect on free oil formation. There was no effect of salt on fat globule size and shape, or on the relative amounts of fat polymorphs ( α , β′ and β crystals). Cooling the cheese at a lower temperature of 0°C after the cooking and stretching stage decreased the amount of free oil and increased expressible serum compared to cooling at 8°C. There was no effect of cooling temperature on the melting point of milk fat in the cheese, however the lower cooling temperature did decrease the relative amount of β′ crystals.

The Rôle of Surface-Active Constituents Involved in the Foaming of Milk and Certain Milk Products. II. Whey, Skimmed Milk, and Their Counterparts

Summary Synthetic solutions of milk proteins and fat have been prepared which duplicate the essential foaming characteristics of whey and skim milk. Lactalbumin and milk fat were found to be the constituents that influence the foaming of whey. The constituents in milk or skim milk that determine its foaming properties are shown to be calcium caseinate, milk fat and lactalbumin. It is considered that calcium caseinate is preferentially adsorbed at the air/liquid interface at temperatures below the melting point of milk fat, lactalbumin being adsorbed at higher temperatures. The presence of milk fat globules is shown to be responsible for the minimum foaming of separated milk at certain temperatures. The addition of milk fat emulsion to blood serum brings about a minimum foaming at room temperatures. Previous work which is not in agreement with the present conclusion is analyzed in the light of the present studies.